The present invention relates to a method of fabricating a semiconductor device and, more particularly, to a method of fabricating a semiconductor device to improve a contact hole gap filling characteristic.
As semiconductor devices shrink, the width of a contact hole is decreased. The width of the contact hole is reduced, whereas the height of the contact hole is increased. Thus, when performing a process of gap filling the contact hole with a conductive layer, the contact hole is not properly gap filled with the conductive layer. Due to this problem, contact short occurs between the contact hole and a bit line. Consequently, erase failure is generated in a device operation and the yield is decreased.
In semiconductor devices of 60 nm or less, tungsten (W) is used as the material of a contact plug. In this case, an adhesion phenomenon occurs in which the tungsten (W) layer is not properly brought in contact with an insulating layer having a contact hole formed therein. Therefore, a titanium (Ti)-based barrier metal layer must be formed in order to prevent the adhesion phenomenon.
However, in a process of depositing the titanium (Ti)-based barrier metal layer within the contact hole, overhang occurs at an upper entry of the contact hole since the width of the contact hole is narrow. At this time, if the contact hole is gap filled with the conductive layer using a subsequent process by narrowing the upper entry of the contact hole in order to prevent such overhang, the contact hole is not fully gap filled with the conductive layer material due to overhang of the barrier metal layer formed at the upper entry of the contact hole, thus generating void. In this state, if a Chemical Mechanical Polishing (CMP) process is performed until the insulating layer is exposed, the void generated within the contact hole is exposed. Consequently, a poor contact problem with a bit line that is formed subsequently is generated.